This application is based on, and claims priority to, Japanese Patent application Patent H10-140922 filed May 22, 1998 in Japan, and which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a disk control device and its method of control for processing data. More particularly, the present invention relates to a disk control device and its method of control by writing data to the disk unit via cache memory or reading the data from the disk unit via the cache memory, to transfer the data to host devices, in response to a disk unit host access, particularly for processing variable-block and fixed-block accesses from host devices.
2. Description of the Related Art
A disk subsystem is equipped with a hard disk unit (DASD, also referred to as Direct Access Storage Device) for data input/output, and with a disk control device. The disk control device is installed between a host device and the hard disk unit to control the writing of data to and the reading of data from a hard disk.
As the device operates mechanically, access time for the hard disk unit is measured in milliseconds, which is considerably slower than access time for semiconductor memory. To increase access speed, the disk control device includes a memory implemented with a cache memory, which is referred to as disk cache architecture.
The cache memory stores data and, thereby, copies frequently accessed data from the host system. If the host system accesses the copied data, data is transferred directly from the cache memory. Disk cache architecture is based on system access data tending to be specific data.
The cache memory holds frequently accessed data because the contents of the memory are replaced according to the Least Recently Used (LRU) algorithm. As mechanical operations are not necessary for frequently accessed data, the I/O response time can be reduced considerably.
A global server comprising a mainframe is used to access a hard disk unit in the variable-block Count Key Data (CKD) format, thereby allowing only a CKD-format disk unit (which is a hard disk drive) to be connected to the hard disk control device.
Fixed Block Architecture (FBA) disk units with SCSI or other interface components, however, are advancing technologically and are soon expected to attain a capacity equivalent to conventional CKDs.
In the fixed-block architecture (FBA) format, all logical blocks (FBA blocks) on a logical device are equal. To overlay the CKD format onto the FBA format one CKD track should be divided into a specified number of FBA blocks. FBA blocks divided from one CKD block are identified with unique identification numbers beginning with 0. A 64KB ID for CKD-FBA format conversion, referred to as CKD ON FBA (COF), is set at the beginning of a divided FBA block.
This logical FBA block is divided into physical FBA blocks for an FBA disk unit, and written onto a disk of the FBA disk unit. A physical FBA block includes an ID at the beginning to store an FBA block address.
As this type of FBA disk unit is compact, low-priced, and efficient, a practical disk control device is available for applying an FBA disk unit to a host device that uses the CKD format.
This disk control device has a function for the mutual conversion of CKD-format data of the host device and FBA-format data of the disk control device. This function realizes access to the FBA disk unit compatible with the CKD format of the host device.
Accordingly, the prior art systems include a disk control device which overlays a CKD format onto an FBA format.
What is needed is a disk control device which allows host computers of either a fixed-block format or a variable-block format to share access to a disk unit of a fixed-block format.
In the field of global servers comprising mainframes, open servers such as UNIX and PC servers are gaining popularity for open systems. If a hard disk subsystem is constructed by connecting an FBA disk unit as an external storage for the mainframe through a disk control device having a CKD-FBA format conversion function, resources are accessed from the global server of the mainframe and are also be shared among UNIX, PC, and other open servers.
When the mainframe (global server) and open servers share resources in a hard disk subsystem, the large-capacity data processing capabilities of the mainframe and the superior processing performance of the open server are utilized for the shared resources.
An object of the present invention is to implement a disk control device component and control method for sharing an FBA disk unit between mainframes (global servers) that use the variable-block format and open servers that use the FBA format and which are host devices.
Another object of the present invention is to provide a disk control device and control method for access utilizing the advantages (which are high performance and reliability) available from host devices that use the variable-block format and the high transaction processing performance available from host devices that use the FBA format.
To accomplish the above-mentioned objects, the present invention is a disk control device comprising a first channel adapter located between a first host device and a disk unit and receiving a variable-block access(CKD)command from the first host device and returning the processing results. The disk control device of the present invention further comprises a second channel adapter located between the second host device and the disk unit and receiving a fixed-block access(FBA) command from the second host device and returning the processing results. In addition, the disk control device of the present invention comprises a device adapter executing an access command from the first or second host device for the disk unit in FBA blocks, a cache memory developing track data as cache blocks in a format that divides a single CKD block into several FBA blocks, a cache function engine controlling the cache memory, and a resources manager managing general resources and controlling processing operations.
The resource manager includes an address conversion unit located at the second channel adapter and converting a fixed-block position address logical block address (LBA) received from the second host device into variable-block position address CCHH.
The resource manager further includes a first controller that calculates an FBA block number of the disk corresponding to variable-block position address CCHH received from the first host device, reads from the disk unit a CKD block containing the FBA block indicated by said FBA block number, develops the block in the cache memory, and searches the cache memory for a record specified by the first host device.
The resource manager also includes a second controller that calculates an FBA block number of the disk corresponding to variable-block position address CCHH received from the second host device, reads from the disk unit a CKD block containing the FBA block indicated by the FBA block number, develops the block in the cache memory, and searches the cache memory for a record specified by the first host device.
The control method of the present invention is included in a disk control device of the present invention comprising a first channel adapter located between a first host device and a disk unit and receiving a variable-block access command from the first host device and returning the processing results, a second channel adapter located between the second host device and the disk unit for receiving a fixed-block access command from the second host device and returning the processing results, a device adapter executing an access command from the first or second host device for the disk unit in FBA blocks, a cache memory developing track data as cache blocks in a format that divides a single CKD block into several FBA blocks, a cache function engine for controlling the cache memory, and a resources manager managing general resources and controlling processing operations.
The control method of the present invention, then, includes a first control process in which a corresponding FBA block number of the disk is determined for a variable-block position address CCHH received from the first host device, a CKD block containing the FBA block of the FBA block number is read from the disk unit and developed in the cache memory, and a cache memory is searched for a record specified by the first host device by referencing the ID correspondence.
The control method of the present invention also includes an address conversion process in which an FBA position address LBA issued from the second host device to the second channel adapter is converted into variable-block position address CCHH.
In addition, the control method of the present invention includes a second control process in which an FBA block number is calculated for a real device corresponding to variable-block position address CCHH obtained during the address conversion process, a CKD block containing the FBA block indicated by the FBA block number is read from the disk unit and developed in the cache memory, and a cache memory is searched for a record specified by the second host device.
These together with other objects and advantages which will be subsequently apparent, reside in the details of construction and operation as more fully hereinafter described and claimed, reference being had to the accompanying drawings forming a part hereof, wherein like numerals refer to like parts throughout.